The present invention relates to a carbon nanotubexe2x80x94based liquid flow sensing device. The present invention also relates to a method for measuring the flow of a liquid using carbon nanotube. More particularly, the present invention relates to a method for measuring the velocity of a liquid along the flow thereof as a function of the current/voltage generated in carbon nanotube due to the flow of the liquid along the surface thereof. In another application, the present invention also relates to a device for the conversion of energy comprising using at least one carbon nanotube and also to a method for the conversion of kinetic energy of a liquid flow into electrical energy using one or more carbon nanotubes.
The measurement of liquid velocity along the direction of flow is of significant importance in several applications. For example, an accurate determination of velocity of ocean or river tides along the direction of the flow is important in predicting tidal patterns, potential weather fluctuations, etc. Other areas where such liquid velocity determination along the flow are of importance include medical applications such as in cardiac and renal therapeutics.
Several methods are known in the art for the measurement of liquid velocity along its flow. For example, one method of low speed flow field velocity determination comprises particle imaging velocimetry, which comprises suspending colloidal particles in the liquid. A fast charge coupled device is provided across the planar cross section of the flow in order to image the colloidal particles. The small seed colloidal particles are illuminated using a laser light sheet. The charge coupled device camera electronically records the light scattered from the particles. Analysis of the image obtained enables determination of the particle separation, and thereby the velocity of the particles.
However, this method has several disadvantages. The primary disadvantage is the underlying assumption that the movement of all the colloidal particles assume the direction of the flow. This is not necessarily true in the case of large sized particles or in the case of very low velocities. Thus, the application of this method is limited to velocities of greater than 0.02 m/s. It is thus, also important in this method, to ensure that the particle size is small enough to ensure that the particle follows the flow of the liquid but at the same time is large enough to effectively scatter light. The equipment required (lasers, CCD cameras) is also large in size. Another disadvantage is that the method is dependant entirely on image analysis and thereby on the analysis algorithms. Since the particle imaging velocimetry method measures the velocity of the colloidal particles and there is no direct digital signal corresponding to the liquid velocity, the flow velocity of pure liquid cannot be measured. The method also is not appropriate for systems where optical access is absent and for liquids that are turbid.
Another method known in the prior art for liquid velocity measurement is Doppler velocimetry which comprises measurement of the Doppler shift of scattered light from micron sized particles suspended in the liquid. The method relies on the fluctuation in the intensity of scattered light received from colloidal particles entrained in a liquid when passing through the intersection of two laser beams. The Doppler shift between the incident and the scattered light is equal to the frequency of the fluctuation of intensity which is therefore proportional to the component of particle velocity lying in the plane of the two laser beams and perpendicular to their bisector. However, this method also suffers from several disadvantages. The method is operable where the particle velocities are greater than 0.001 m/sec. This method also requires large and expensive equipment such as a plurality of lasers and digital counters. Another significant disadvantage of this method is that it is restricted to a single point measurement with the data obtained being completely dependant on the particle arrival in the measuring volume and not on user requirements. Particle velocity and its derivatives differ in vortex cores and across shocks. Similar to particle imaging velocimetry, this method also requires that the particle size be small enough to flow along the liquid flow path easily but large enough to produce the required signal above the noise threshold. This method also does not work in systems where optical access to the liquid flow path at the measurement volume is absent. Signal level depends on the detector solid angle. As a result while the Mie scattering intensity is substantially better in the forward direction, it is difficult to set up forward receiving optics which remain aligned to the moving measurement volume. Greater noise at higher speed with radio frequency interference is possible. Again, similar to the PIV method, the flow velocity of unseeded liquids cannot be measured since there is no direct digital signal corresponding to the liquid velocity. This method is appropriate only for liquids containing colloidal particles and not for clear liquids.
Another known method to measure fluid velocity comprises the measurement of heat transfer change using a electrically heated sensor such as a wire or a thin film maintained at a constant predetermined temperature using an electronic control circuit. The heat sensor is exposed to the fluid whose velocity measurement is to be taken. The fluid flowing past the sensor cools the heat sensor which is compensated by the an increased current flow from the electronic control circuit. Thus, the flow velocity of the fluid can be measured as a function of the compensating current imparted to the heat by the electronic control circuit. However, in this method a slight variation in the temperature, pressure or composition of the fluid under study can result in erroneous readings. In order to maintain a relatively accurate measurement from the heat sensor, it is also necessary to provide complicated compensating electronics for constantly calibrating the sensor against any change in environmental parameters. In addition, even such compensating electronics can be subject to error. The sensor generally is operable at fluid velocities of greater than 0.01 m/s and not for very low velocities. At low velocities, the convection currents in the liquid cause a malfunction in the sensor.
Another method of liquid velocity measurement comprises calculating the velocity of the liquid flow as a function of vortices created downstream in the liquid using a bluff body or a shedder bar. The vortices are counted using piezoelectric sensors or ultrasonic sensors. This method is useful for measuring only flow rates greater than 0.001 L/s. The method focuses on measuring volumetric flow rates and not directly measuring flow velocities. Thus while useful for small flow rates, the device is not appropriate for liquids with high viscosity.
It is also known to calculate flow liquid velocity in high viscosity liquids using a plurality of pairs of piezo-resistive pressure sensors across an integrated fluid restriction in order to measure the differential pressure. However, while this device is operable at flow rates of the rate of a few xcexcL/s, the volumetric flow rates and not flow velocities are measured. Also, this method is suitable for measurement of small flow rates only.
Yet another method for the measurement of flow velocities comprises the use of rotary flow meters which work on an arrangement of turbine wheels. The motion of the liquid through the turbine, otherwise called the rotor wheel, causes the turbine to rotate. The rotational frequency of the rotor wheel depends on the velocity of the liquid and is measured using either an electro-optical system or by electronically sensing the square wave pulse generated by magnets embedded in the turbine vanes. The size of the sensor arrangement is also to the order of 50 cm3. The rotary flow meter is suitable for use in cooling systems irrespective of the nature of the liquid (clear or turbid) where measurement of large flow rates of over L/sec and the accuracy of the measurement of directionality of the liquid motion is about 50%. That is to say, the sensor can determine if the liquid is flowing in the forward or reverse direction.
As can be seen from the above discussion, the various methods known in the art for the measurement of flow velocities suffer from various disadvantages. Both particle imaging velocimetry and Doppler velocimetry require optical access and use lasers. The equipment size is also large rendering it expensive. Thermal anemometry requires large volumes of liquids in order to minimize convection currents and generally is suitable only for large velocities of greater than 0.01 m/sec. Thus it is not suitable for biological systems which involve small volumes of liquid flowing at low flow velocity. Rotary flow meters, pressure sensors and vortex flow sensors do not measure the flow velocities directly but rather the volumetric flow rates.
Another important area of investigation is the conversion of energy and energy conversion devices which are economical and possess a long life. One example of such an area is with respect to cardiac pacemakers. Cardiac pacing requires the periodical electrical simulation of the heart in order to control the timing and contractions thereof. Stimulation is for example obtained by electrical pulses generated by a cardiac pacemaker. It is for example known to measure cardiac performance using an internally implanted flow sensor. The flow sensor measures the blood velocity and communicates the information to the pacemaker which in turn estimates cardiac output in order to determine whether the blood flow pattern is abnormal and requires correction. It is also known to use flow sensors with implanted defibrillators which on verification of the absence of a heart beat in a patient apply a shock to the heat to restart the heart. Traditional flow sensors used in the field of cardiac pacemakers or defibrillators are discussed for example in U.S. Pat. No. 5,174,299. This disclosure teaches the use of a thermocouple to measure the velocity of blood flow. The flow sensor comprises two tubes of the same metal joined to each other through a middle tube of another metal. This forms two junctions. Wires are connected to the two junctions in order to convey a voltage to the pacemaker corresponding to the temperature difference between the two junctions. However, this device suffers from several limitations such as the inability to distinguish between forward, reverse and cross flow. Another disadvantage of this flow sensor is that a plurality of wires are required, for example for carrying the output voltage to the pacemaker and another pair to heat the flow sensor. An attempt to overcome this problem has been made in U.S. Pat. No. 5,831,159 which discloses the use of a plurality of thermocouples in series connection in the form of a thermopile as the flow sensor. The thermocouples comprise of two conductors of different metals joined together to form a junction. The unique construction of this device avoids the problems of plurality of wires by using the same wire pair as both the heat source for the thermopile as well as well as for carrying the current output to the pacemaker or defibrillator. However, the problem of an external power source to heat the thermopile is not avoided. The construction of this device is also quite complex and expensive. Neither of the two devices discussed immediately above provides a solution for battery replacement in the pacemaker or defibrillator itself.
Another area where energy conversion devices are required is for supply of electricity for domestic and industrial use. Currently, the demand for electrical energy worldwide is met by one of three sources: nuclear power, thermal power and hydroelectric power. Nuclear power plants require expensive safety equipment and measures in view of the potential for radiation leakage. Thermal power plants use fossil fuels which result in the attendant problems of pollution and also suffer from reduced supplies due to depletion of fossil fuels and oil. Hydroelectric power requires large dams to be constructed and is completely dependant on water flow in a river or any other water source. The equipment required is also expensive and occupies a large area. Of the various devices and methods of flow velocity measurement, only one, namely rotary flow sensor can actually also generate electricity due to the action of the liquid flow across the turbine blades. However, the magnitude of the power generated in relation to the size of the device renders it unsuitable for use for large scale energy conversion.
It would therefore be useful to develop a device which is capable of both measurement of flow velocities of a low range irrespective of the nature of the liquid and also as an energy conversion device irrespective of the scale of energy required.
The main object of the invention is to provide a flow sensor which is operable even at very low flow velocities of 10xe2x88x928 m/s with accuracy in measurement and low response times of 0.01 seconds.
It is a further object of the invention to provide a flow sensing device which by its simplicity and small size of construction is economical, does not result in any turbulence in the liquid flow thereby ensuring accuracy in flow velocity measurement, and is impervious to variations in external parameters such as liquid or ambient temperature, pressure differential or viscosity.
It is another object of the invention to provide a flow sensing device which is operable irrespective of the nature of the liquid (whether clear or turbid, high or low viscosity) with accuracy in measurement and low response times of  less than 0.1 seconds.
A further object of the invention is to provide a flow sensor device that does not require any external source of power for its operation.
It is another object of the invention to provide a flow sensing device which can determine the directionality of the liquid flow.
It is yet another object of the invention to provide a method for the determination of flow velocity of all liquids irrespective of their nature which does not require optical access, is operable even at low flow velocities of 10xe2x88x928 m/s, irrespective of flow volumes, and is capable of biomedical applications.
It is yet another object of the invention to provide a method for the determination of flow velocities which does not require any external seeding with colloidal particles of determinate size in the liquid and is not susceptible to variations in external parameters such as liquid temperature, pressures at a particulate flow plane or viscosity.
It is another object of the invention to provide a flow sensor device capable of utilization as an energy conversion device capable of generating electrical energy based on liquid flow.
It is a further object of the invention to provide an energy conversion device which by its simplicity of construction is economical, does not result in any turbulence in the liquid flow thereby ensuring accuracy in flow velocity measurement, and is impervious to variations in external parameters such as liquid or ambient temperature, pressure differential or viscosity.
A further object of the invention is to provide an energy conversion device that does not require any external source of power for its operation.
Another object of the invention is to provide a method for the generation of electricity without reliance on any nuclear, thermal or hydroelectric power source and based purely on the flow of a liquid.
The above and other objects of the invention are related by the device of the invention which comprises the use of carbon nanotubes, whether single wall type of multi wall type as flow sensors. Both methods of the invention, namely, liquid flow velocity measurement and energy conversion are based on the induction of current/voltage in a carbon nanotube due to the flow of a liquid along its surface and along the direction of the flow.
Accordingly, the present invention provides a flow sensing device useful for measurement of liquid flow velocities irrespective of the flow velocity or the nature of the liquid, said device comprising at least one carbon nanotubes, each end of the at least one carbon nanotube being connected at each end thereof through at least a conducting element to a electricity measurement means.
In one embodiment of the invention, the carbon nanotube is a single wall type carbon nanotube.
In another embodiment of the invention, the carbon nanotube is of the material type carbon nanotube.
In a further embodiment of the invention, the electricity measurement means comprise a ammeter to measure the current generated across the opposite ends of said at least one or more carbon nanotube or a voltmeter to measure the potential difference across the two opposite ends of the said one or more carbon nanotube.
In another embodiment of the invention, the flow sensing device comprises of a plurality of carbon nanotubes all connected in series or parallel with a single conducting element each being provided at the respective extreme ends of the said plurality of carbon nanotubes.
In a further embodiment of the invention, the said plurality of carbon nanotubes are connected in series so as to measure the potential difference generated across the ends of the said plurality of carbon nanotubes.
In yet another embodiment of the invention, the said plurality of nanotubes are connected in parallel to each other so as to enable determination of the current generated across the two ohmic contacts formed by the respective conducting elements at the ends thereof.
In yet another embodiment of the invention, the conducting elements of the flow sensing device are provided with a protective insulating coating to prevent electrical contact with the liquid.
In yet another embodiment of the invention, the flow sensing device is provided on a insulated base.
In one embodiment of the invention, the conducting element comprises of a wire.
In one embodiment of the invention, the conducting element comprises of an electrode.
In yet another embodiment of the invention, the conducting element comprises of a combination of a wire connected to an electrode.
In another embodiment of the invention, the liquid whose flow velocity is determined is flowing water.
In yet another embodiment of the invention, the liquid is a biological fluid such as blood.
The invention also relates to a method for the determination of liquid flow velocities irrespective of the nature of the liquid or the flow velocity thereof, which comprises measuring in said liquid a flow sensing device comprising of at least one carbon nanotube connected at each thereof through at least a conducting element to a electricity measurement means, the liquid flow over said at least one carbon nanotube generating a flow of electricity along the direction of the liquid flow by forcing free charges present in the said at least one nanotube, said electrical energy being transmitted by said conducting element to said electricity measurement means provided external to the liquid flow, to measure the electricity generated as a function of the rate of flow of said liquid.
In one embodiment of the invention, the liquid comprises a polar liquid.
In a further embodiment of the invention, the polar liquid is selected from water and a biological fluid. The biological fluid may preferably be blood.
In another embodiment of the invention, the liquid comprises a non-polar liquid.
In a further embodiment of the invention, the non-polar liquid is selected from methanol, ethanol, and other non-polar liquid.
In one embodiment of the invention, the carbon nanotube is a single wall type carbon nanotube.
In another embodiment of the invention, the carbon nanotube is of the multiwall type carbon nanotube.
In a further embodiment of the invention, wherein the foregoing of the free charges is along the direction of the liquid flow due to the Coulombic interaction between the Coulombic field of the liquid and the free charges, thereby ensuring that only velocity along the direction of the liquid flow is determined.
In another embodiment of the invention, the immersion of the said at least one carbon nanotube in the liquid at rest generates a rest voltage in the nanotube, the exact velocity of the liquid flow being calculated as a function of the voltage generated in the carbon nanotube during flow after deduction of the rest voltage.
In another embodiment of the invention, the response time of the flow sensing device is less than 0.01 seconds.
The invention also relates to an energy conversion device comprising a energy generation means comprising one or more carbon nanotubes, each said one or more nanotube comprising of at least one carbon nanotube connected at each end thereof through at least a conducting element to a electricity storage or usage means to store or use the electricity generated in the said one or more carbon nanotubes due to the liquid flow along the surface thereof.
In one embodiment of the invention, the carbon nanotube as a single wall type carbon nanotube.
In another embodiment of the invention, the carbon nanotube is of the multiwall type carbon nanotube.
In one embodiment of the invention, the energy generation means comprises a plurality of carbon nanotubes.
In a further embodiment of the invention, the said plurality of carbon nanotubes are connected in series.
In a further embodiment of the invention, the said plurality of nanotubes are connected in parallel.
In yet another embodiment of the invention, the conducting elements of the energy conversion means are provided with a protective insulating coating to prevent electrical contact with the liquid, thereby ensuring that accidental discharge of electricity generated due to liquid flow along the surface thereof to the liquid does not occur.
In yet another embodiment of the invention, the energy conversion means is provided on an insulated base.
In another embodiment of the invention, the energy storage means comprises of a battery or storage cell.
In one embodiment of the invention, the conducting element comprises of a wire.
In a further embodiment of the invention, the conducting element comprises of an electrode.
In yet another embodiment of the invention, the conducting element comprises of a combination of a wire connected to an electrode.
In another embodiment of the invention, the liquid whose flow velocity is determined is flowing water.
In yet another embodiment of the invention, the liquid is a biological fluid such as blood.
The invention also relates to method for the generation of electrical energy using an energy conversion device comprising a energy generation means comprising one or more carbon nanotubes, each said one or more nanotube comprising of at least one carbon nanotube connected at each end thereof through at least a conducting element to a electricity storage or usage means, the flow of the liquid along the surface of the energy conversion means forcing the free charges in the said one or more carbon nanotubes to flow along the direction of the liquid flow, thereby generating electrical energy, said electrical energy being transmitted to the energy storage or usage means through the said conducting elements.
In one embodiment of the invention, the carbon nanotube is a single wall type carbon nanotube.
In another embodiment of the invention, the carbon nanotube is of the multiwall type carbon nanotube.
In one embodiment of the invention, the energy generation means comprises a plurality of carbon nanotubes.
In a further embodiment of the invention, the said plurality of carbon nanotubes are connected in series.
In yet another embodiment of the invention, the said plurality of nanotubes are connected in parallel.
In yet another embodiment of the invention, the conducting elements of the energy conversion means is provided with a protective insulating coating to prevent electrical contact with the liquid, thereby ensuring that accidental discharge of electricity generated due to liquid flow along the surface thereof to the liquid does not occur.
In yet another embodiment of the invention, the energy conversion means is provided on an insulated base.
In another embodiment of the invention, the energy storage means comprises of a battery or storage cell.
In another embodiment of the invention, the battery is a battery of a cardiac pacemaker device.